Expand. If necessary, combine like terms. $(2+7x)(2-7x)=$
Notice that this expression has the following special form: $(a+b)(a-b)$ This form expands to what we call "a difference of squares": $( a+ b)( a- b)= a^2- b^2$ Using the above pattern, we get: $\begin{aligned} ( 2+{7x})( 2-{7x})&= 2^2-({7x})^2 \\\\ &=4-49x^2 \end{aligned}$